1. Field of Invention
The present invention relates to integrated circuit structures and fabrication methods, and in particular to enhancing tungsten nitride adhesion to an underlying dielectric.
2. Related Art
The semiconductor industry is moving toward copper interconnects to produce faster and less expensive integrated circuits. However, manufacturing fully integrated copper devices presents formidable technical challenges. One critical manufacturing aspect is the choice of barrier material. Copper readily diffuses into interlayer dielectrics, and the diffusion may result in line-to-line leakage and integrated circuit device damage.
Physical vapor deposited (PVD) tantalum (Ta) and tantalum nitride (TaN) liners have been experimented with as copper barriers for 0.25 .mu.m and 0.18 .mu.m device generations. These materials have a nearly amorphous texture that impedes copper diffusion. However, the drawback of the PVD techniques, including ionized PVD, is poor sidewall coverage in high aspect ratio, dual damascene features. The industry requires conformal, highly reliable copper barriers.
Tungsten nitride is a potential copper barrier. When deposited using plasma enhanced chemical vapor deposition (PECVD), tungsten nitride provides good conformal coverage in high aspect ratio features. Unfortunately, tungsten nitride is not thermally stable when deposited on dielectric materials such as silicon dioxide. During high temperature process steps (e.g., annealing after electrochemical plating of copper) following the tungsten nitride deposition, the tungsten nitride separates from the dielectric. What is required is a method to improve the tungsten nitride's thermal stability and adhesion to the underlying dielectric.